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A comparative analysis of nutrient utilisation and meat quality parameters of boer goats and South African mutton merinos

Sheridan, Rouxlene (2001-12)

Thesis (MScAgric)--University of Stellenbosch, 2001.

Thesis

ENGLISH ABSTRACT: One of the reasons why meat supply does not meet human demand is that man has
concentrated on utilising relatively few animal species as a source of meat. Development of
unconventional livestock, such as goats, is advocated as a means of increasing global meat
production and consumption. Although South Africa possesses large numbers of domestic
ruminants, meat consumption has been limited mainly to sheep and cattle. Goats are used to
a lesser extent. This is partly attributed to a general belief that goat meat is inferior to mutton
and beef.
Numerous contradictions regarding comparative goat and sheep growth, carcass
characteristics and meat composition exist in literature. Concepts involved with most of the
contradictions includes average daHy gain (ADG), dressing percentage, carcass weight
distribution and organoleptic characteristics, especially tenderness, juiciness and flavour,
particularly as pertaining to animals reared/grown under intensive/feedlot conditions.
Therefore this project was undertaken to obtain more information on the growth, carcass and
organoleptic characteristics, as well as meat chemical compositions of Boer goat (BG) kids in
comparison with South African Mutton merino (MM) lambs, reared under feedlot conditions.
Thirty-two BG kids and 32 MM lambs were used for this investigation. All the animals were
castrated and weaned before entering the feedlot. Two pelleted diets (fed to 16
animals/species) with either a low (LE; 8.9 MJ/kg OM) or a high (HE, 10.9 MJ/kg OM)
metabolisabie energy level were fed individually, ad lib for either 28 or 56 days. Feed and
water intake, ADG and feed conversion efficiencies (FCE) were monitored. During the last week of the feeding trial, 12 BG kids and 12 MM lambs were used to evaluate the digestibility
of the two diets.
After either 28 or 56 days, the animals were slaughtered and the carcasses dissected into
South African commercial cuts. The m. semimembranosus and 8-9-10-rib cut of each carcass
was dissected for determination of chemical composition, drip loss, cooking loss, shear force
values and colour measurement. The m. gracilis was dissected from the hind leg of the
carcass and used for sensory evaluation.
MM's had significantly higher AOG's than BG's (e.g. MMHE56: 0.281; BGHE56: 0.162
kg/day). Within a diet there was no difference (P>0.05) in FCE between BG's and MM's and
only the MM's FCE differed between the LE and HE diet (e.g. BGLE28: 7.65; BGHE28: 6.37;
MMLE28: 8.73; MMHE28: 5.56 kg feed/kg weight gain). BGLE digested dry matter (OM),
crude protein (CP) and energy more efficiently and had a higher energy retention than MMLE.
The two diets had the same ME-value for the goats, which confirms that goats perform equally
well on a lower quality feed as their contemporaries on a higher quality feed. Neither species,
nor diet affected nitrogen retention. The BG had a 49 % lower (P<0.01) water intake per kg
weight gain than the MM on both the high and low energy diets. Both species had a lower
(P<0.01) water intake on the high than on the low energy diet. Furthermore, the BG had a
daily water intake of only 171 ml/kgo.75 compared to the 302 ml/kgo.75 of the MM.
The weight of the liver, empty stomach, head and feet (as a percentage of empty body weight)
were higher in goats than in sheep. The MM's had significantly heavier skins, probably due to
wool growth. Both kidney fat and gastro-intestinal tract (GIT) fat increased with age. The
animals slaughtered after 56 days in the feedlot had significantly longer and deeper carcasses
than their contemporaries slaughtered after 28 days. Within a diet and slaughter age, the MM
had significantly broader and deeper carcasses than the BG's. BG's had significantly less
weight per unit carcass length, and thus more slender carcasses than MM's. Diet had no
significant influence on the carcass weight distribution of the goats. However, MM's had
heavier carcasses (LE: 19.87 vs. 15.28 kg; HE: 24.01 vs. 17.05 kg) and proportionally heavier
ribs and buttocks than BG's.
Neither diet nor slaughter age influenced the proximate analysis of the m. semimembranosus,
but MM's had significantly lower moisture values than BG's. In the 8-9-10-rib cuts BG's had
significantly more moisture and protein and lower fat and energy values than MM's. OM, fat
and energy values increased with an increase in slaughter age in both species. BG's had
significantly higher concentrations of 11 of the 18 measured essential amino acids in their 8-9-
10-rib cuts than the MM's. Gaat carcasses had higher Ca, K, Mg, Na and P-Ievels than sheep
carcasses, regardless of the diet fed. There was a tendency for goat's m. semimembranosus
to have a lower Fe-content than that of sheep. BG carcasses had a lower carcass cholesterol content than that of lamb (66.77 vs. 99.28
mg/100g, respectively). Palmitic (C16:0), stearic (C18:0) and oleic (C18:1 n9) acid comprised
the greatest proportions of fatty acids in both the m. semimembranosus and 8-9-10-rib cut for
both species. On a LE-diet there was no significant difference between the saturated fatty
acid (SFA) to unsaturated fatty acid (UFA) ratio of goat meat and lamb. However, on the HEdiet,
lamb had a significantly higher SFA:UFA ratio than chevon (m. semimembranosus: 0.842
vs. 0.689; 8-9-10-rib cut: 1.407 vs. 0.892). Organoleptically, a difference was noted between
chevon and lamb. Each has a specific species flavour, which was not influenced by energy
level of the diet. BG meat was perceived to be stringier than that of the MM, but there was no
significant difference in Warner-Bratzler shear force values. Tenderness declined with age in
both species and there was also a tendency for goat meat to be less juicy than lamb. Chevon
had a more pronounced aftertaste than lamb. No objective differences could be distinguished
between the colour of the cooked chevon and lamb. There was a tendency for fresh lamb to
have a higher a*-value (redness) than chevon. Although diet did not influence drip loss, drip
loss increased with an increase in slaughter age. Only after 56 days did the MM's m.
semimembranosus have a significantly higher drip loss than the BG's (LE: 4.84 vs. 3.43%;
HE: 4.72 vs. 3.32%). In the m. semimembranosus of both species, cooking loss increased
with an increase in slaughter age.
Since diet did not influence the growth, carcass weight distribution, water holding capacity,
colour, shear force values or organoleptic qualities of chevon, BG's may be finished on a diet
with a lower ME-value than that usually formulated for sheep, without a reduction in
performance. This may render a direct economic advantage for BG feedlot finishing. Meat
from young feedlot goats is not inferior to that of lamb and it has a higher protein percentage
and lower fat percentage. Therefore, it can be considered as a healthy food commodity,
especially among low-income groups or people wishing to consume a low calorie diet.